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Old 01-11-2007, 11:27 AM   #1
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Default Adding slugs to cranks

Well I am curious as to what purpose putting slugs in the cranks serve ?? Why would you want to increase the weight of a crankshaft.... I understand the heory of balasncing, but since its a single cylinder engine I am thinking the slugs serve other purposes as well... does having more weight on the trailing side of the couterweight serve another purpose.... I have the ability and tools to slug a crank, I just dont know what purpose it serves, and to be honest I dont have a clue how to determine where to put the weight...Anyways any help or knowledge on this would be greatly appreciated...
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Old 01-12-2007, 03:25 PM   #2
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Default Slugs

I think it's done because you can grind alot of steel off then add heavier slugs to rebalance.
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Old 01-12-2007, 03:53 PM   #3
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My understanding is they cut the heavy metal out and replace it with a lighter material.
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Old 01-12-2007, 04:40 PM   #4
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Quote:
Originally Posted by Maximo
Well I am curious as to what purpose putting slugs in the cranks serve ?? Why would you want to increase the weight of a crankshaft.... I understand the heory of balasncing, but since its a single cylinder engine I am thinking the slugs serve other purposes as well... does having more weight on the trailing side of the couterweight serve another purpose.... I have the ability and tools to slug a crank, I just dont know what purpose it serves, and to be honest I dont have a clue how to determine where to put the weight...Anyways any help or knowledge on this would be greatly appreciated...
Slugs are sometimes added to engines to make better balance. A heavy metal is used such as tungsten. First you must figure out exactly where to put the slug. , then the hard part.
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Old 01-12-2007, 06:53 PM   #5
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It's called balance factor and different balance factors have different effects in power delivery than others. Basically the balance factor is how much weight of the crankshafts counterweight is required to counteract the weight of the piston, pin, clips and the top 50% of the connecting rod. A balance factor from 52% up to 65% is practical and lower or higher numbers will give different feel to the engine. This practice is not to be confused with crankshaft balance however, although it is directly related, they have slightly different effects. Unfortuantely, a single cyl engine cannot be dynamically balanced and therefore will always have vibration. The goal is to lessen the vibration in the rpm range that the peak power is desired so the engine won't fight itself in that range.

There are other factors that need to be taken into acct. such as connecting rod mean tq angle, connecting rod length, piston dwell, etc. but this gets really involved in the math dept.

Some time ago there was a pretty good thread on this forum relating to crank balance that might be a good read with lots of info if someone were so inclined to look it up. I posted some drawings of how to measure balance factor.

Good luck, but with this one, I feel it might be a stone better left unturned unless you have some spare engines and crankshafts to waste on trial and error.

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Old 01-12-2007, 07:20 PM   #6
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Hey MX Wrench , do you think you can find that one ? id be interested in reading up on it. Also is nitrodyne your company ? whats the damage on an engine dyno ? do you do chassis dynos too ?
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Old 01-12-2007, 07:42 PM   #7
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Quote:
Originally Posted by MassiveMods
Hey MX Wrench , do you think you can find that one ? id be interested in reading up on it. Also is nitrodyne your company ? whats the damage on an engine dyno ? do you do chassis dynos too ?
http://www.rctech.net/forum/showthre...kshaft+balance

And yes, Nitrodyne Systems is my company. The dyno's are selling for approx. $6500 depending on what options are installed. And sorry, no chassis dynos in the works.

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Old 01-12-2007, 08:52 PM   #8
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Well I am not scared to do that kind of mod really.... I do feel i have some solid skills with my hands and I have pretty good tooling...I dont care if i waste some cranks either.... But i still dont know the true balancing numbers so I suspect some bumps along the way

heres my new heavy duty Dremel i bought

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Old 01-13-2007, 07:33 AM   #9
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thats your dremel? how will you ever fit that in your pit bag on the weekends?
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Old 01-13-2007, 09:49 AM   #10
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thats your dremel? how will you ever fit that in your pit bag on the weekends?

I have a very big Carry bag LOL
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Old 01-13-2007, 02:55 PM   #11
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Hey Maximo , Dont forget the 6 inch angle grinder on the tool rack ! Whenever you wanna go free style go the grinder ! lol
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Old 01-14-2007, 01:37 AM   #12
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I found the angle grinder was a little to slow for me !!
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Old 01-16-2007, 12:30 AM   #13
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Quote:
Originally Posted by Maximo
Well I am not scared to do that kind of mod really.... I do feel i have some solid skills with my hands and I have pretty good tooling...I dont care if i waste some cranks either.... But i still dont know the true balancing numbers so I suspect some bumps along the way

heres my new heavy duty Dremel i bought

so i be seeing more of this mod again ... sts crank mod
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